Abstract
: Aggregate shape and texture affect shear strength of granular materials by influencing the particle interlock and the load distribution properties. The objective of this study was to investigate the influence of grain shape, angularity and surface texture on the deformation properties of unbound granular materials. Only one type of granular material was tested in the laboratory, gneiss from Askøy outside Bergen, Norway. This is a hard-rock, commonly used in road construction in Norway. To study the effect of grain shape and texture only, the same test procedures were consistently followed for a given level of compaction. By choosing a uniformly-graded material, it was expected that the impact of grain shape would be more pronounced and discernible. Aggregate samples with four different particle shape characteristics were produced from the Askøy gneiss. Both flat and cubical aggregates were obtained from various stages in the crushing process. The texture and angularity properties were also changed by wearing the crushed rock in the Nordic ball mill test drum. A three-dimensional (3-D) image analysis approach was adopted for an accurate characterization of the grain shape, texture and angularity properties. The aggregate samples were tested for resilient modulus and permanent deformation characteristics by applying a multistage loading procedure using the cyclic load triaxial test. The cubical aggregates were easier to compact when compared to the flaky aggregates. The cubical rounded aggregates gave the highest resilient moduli when tested at high stress levels. For the cubical aggregates, the angularity and surface texture seemed to have a significant effect on both the elastic and plastic shakedown threshold limits.
